1. Field of the Invention
The invention relates to a polyaxial bone anchoring device including a bone anchoring element for anchoring in a bone or a vertebra, a head receiving part for receiving a head of the bone anchoring element, a locking ring mounted around the head receiving part for coupling a stabilization rod to the head receiving part and to the bone anchoring element, and a cap with a locking element for securing the rod and for locking the assembly. When the rod is mounted in a rod receiving portion of the locking ring and the cap is placed onto the assembly, the cap is rotatable with respect to the head receiving part between a first position in which the cap is out of engagement with the head receiving part and a second position in which the cap engages the head receiving part. The locking element exerts pressure onto the rod to move the locking ring to a position where the locking ring locks the head in the head receiving part. Simultaneously, the rod can be fixed by the locking element.
2. Description of Related Art
US 2009/0149887 A1 describes an apparatus for connecting a bone anchor to a support rod including a connector body, a sleeve around the connector body and a cap.
US 2011/0213419 A1 describes a screw and rod fixation assembly including a body member including a screw seat for seating a screw head therein and a rod seat for seating a rod therein. An adjustable locking ring applies a locking force against the screw head seated in the screw seat and a locking cap adjustably applies a locking force against a rod seated in the rod seat. The adjustable screw locking ring and locking cap function independent of each other.